Large scale displays are constructed with direct-type backlight module. The direct-type backlight modules are built with light emitting diodes (LEDs) and their lens. The luminance is distributed from the center outwards and the light escaping outwards should be even in quality. FIG. 1 illustrates a luminance simulation diagram of a current LED of a prior art. The luminance is unequally distributed from the center toward the surrounding that results in uneven lights existing from the direct-type backlight module and bad display quality.